Visible indicators, often called tell-tale lights, are common on instrument clusters found in vehicles. Examples include fog lamp indicators, bright headlight indicators, and engine malfunction warning indicators. The visual indicators notify the operator of operational problems and/or the operational status of vehicle systems.
A hole is typically cut or stamped in the instrument cluster in a shape of the desired indicator. A colored lens is placed over the hole. When active, a light bulb behind the instrument cluster shines through the colored lens. Conventional visible indicators tend to be aesthetically displeasing because they leave a visible stenciled dark spot that can be seen on the instrument cluster in daylight when the visible indicator is inactive.
Currently, instrument clusters backlit with electroluminescent (EL) film are being used. These instrument clusters use a sheet that is cut to the shape of the visible indicator. Alternately, a silk-screened blackout is placed over the EL film. These approaches also leave a visible dark spot in daylight when the visible indicator is inactive. These approaches also prevent the EL film and visible indicator from being two different colors.
Liquid Crystal Display (LCD) screens can also be used. The LCD screens are located in the EL sheet mounting layer and are driven by a computer. The 256 color palette of the LCD does usually not create a color that matches the inherent luminescent property of the EL film. When the LCD is switched off, a large dark square can be seen. LCD screen types have similar aspect ratios, which prevents some forms of visible indicator location and design. Some LCD screens also include components that are not yet approved for automotive purposes.
In another approach, a hole is made in the EL film. A backlight generates the visible indicator. Usually, the hole is stamped or cut. These methods are not desirable because the EL film is composed of several laminated layers. If disturbed, the layers will open the layered circuit locally and create a dark spot around the visible indicator. Also, shear stress during cutting can cause delamination, particularly at right angle turns in the cutter path. The driver can see the stenciled hole in the EL film in daylight when the visible indicator is inactive.